1. Field of the Invention
This invention relates generally to a technique for mapping standard ATM service classes into a media access control channel and, more particularly, to a technique for mapping standard ATM service classes coded for wired transmissions into a media access control channel using a media access control layer in a wireless communications system, such as a satellite communications network.
2. Discussion of the Related Art
Various satellite communications systems, such as Ka-band satellite communications networks, make use of processing satellites orbiting the Earth in a geosynchronous orbit. As is known in the art, processing satellites provide the wireless transfer of data between user Earth terminals (UET) at ground stations on the Earth. Data is transmitted to the satellite from a source UET on a satellite uplink. The uplink signals are transmitted on channel slots that are separated in frequency and time. The data that is transmitted on the channel slots is typically separated or packaged into separate ATM (asynchronous transfer mode) data cells, as is well understood in the art. The ATM cells are demodulated, decoded and switched at the processing satellite, and then transmitted back to Earth on a satellite downlink to a destination UET. A suitable antenna system is provided on the satellite to receive the uplink signals and transmit the downlink signals over a predetermined coverage area on the Earth.
Terrestrial ATM switches used in the transfer of ATM data cells in wired ATM communications networks on the Earth are usually connected directly by point-to-point wires or fiber-optic cables. The data to be transmitted is configured into the ATM data cells in an ATM layer within the terminal processor. In most types of wired systems, the ATM data cells can be directly transmitted by what is referred to in the art as the physical layer. The physical layer is the data transmission mechanism, such as a modem, that converts digital bits to an analog waveform for transmission over a wire, fiber or a satellite (i.e., transferred between the terminals). Additional processing may be required in the physical layer for a broadcast medium that uses some form of multiple access control, such as multi-frequency time-division multiple access (MF-TDMA), in the physical layer. A discussion of wireless ATM network protocol stacks can be found in Raychaudhuri, Dipankar, xe2x80x9cWireless ATM Networks: Architecture System Design and Prototyping,xe2x80x9d0 IEEE Personal Communications, August 1996, pgs 42-49.
For wireless communications networks, such as satellite communications networks, a media access control (MAC) layer is required between the ATM layer and the physical layer to satisfy the dynamic nature of the ATM protocol and the multi-media traffic it carries to provide additional processing between the ATM layer and the physical layer, because the ATM protocol was not originally designed to operate over a broadcast medium. For example, a different MAC channel may be required for the wireless transmission of the various ATM services classes, including information to gain access to the network (to sign on); signaling information to send up a call or connection (call routing); signaling information to tear down a call; signaling information to change the required configuration of a call; control information to configure the on-board payload of the satellite; ATM constant bit-rate (CBR) sources; ATM real-time variable bit-rate (rt-VBR) sources; ATM non-real time variable bit-rate (nrt-VBR) sources; ATM available bit-rate (ABR) sources; and ATM unspecified bit-rate (UBR) sources. The MAC layer allows the ATM layer to operate seamlessly over the satellite network. Currently, the use of MAC layers in commercial satellites do not exist.
The traffic characteristics of the different ATM service classes dictates the need for different multiple access protocols for efficient transport. For example, virtual private networks and web surfing applications will use the ABR or UBR service classes. In these examples, the traffic displays large peaks followed by periods of idle time; therefore this type of traffic requires some type of demand assigned multiple access (DAMA) protocol for efficient use of the bandwidth resource.
What is needed then is a strategy for mapping the standard ATM service classes in the ATM layer into one of a plurality of available MAC channels in the MAC layer that enables the ATM data cells to be efficiently transmitted over a satellite physical layer. It is therefore an objective of the present invention to provide such a mapping scheme.
In accordance with the teachings of the present invention, a mapping scheme is disclosed that maps standard ATM service classes of the type used in a wired communications network into one of a plurality of available media access control channels that allows the particular ATM protocol to be transmitted efficiently over a wireless communications system, such as a satellite network. The various media access control channel types reside in a media access control layer between the ATM layer and the physical layer. A predetermined uplink user protocol is assigned to each MAC channel to efficiently transmit the ATM cells on the satellite uplink.
The available media access control channel types in the media access control layer include network access channels (NAC), dedicated channels (DC), time dedicated channels (TDC), fair broadband shared data channels (FB-SDC), shared reservation channels, first-come first-served shared data channels (FCFS-SDC), and narrowband shared data channels (N-SDC). The particular transmission protocol for each MAC channel is selected from a slotted aloha protocol, a fixed channel-slot assignment protocol, a finite-duration fixed channel-slot assignment protocol, a centralized broadband fair demand assigned multiple access protocol, a centralized demand assigned multiple access protocol and a distributed demand assigned multiple access protocol.
Additional objects, advantages, and features of the present invention will become apparent in the following description and appended claims, taken in conjunction with the accompanying drawings.